Method of making transfer sheet



Dec. 16, 1969 E. STRAUSS ETA!- 3,434,254

' METHOD OF MAKING TRANSFER smzm Filed Oct. 18. 1967 F/GJ Has! United States Patent US. Cl. 11736.1 13 Claims ABSTRACT OF THE DISCLOSURE A copy sheet having a transfer layer of desired color which may differ from the color of the copy produced by transferring part of the transfer layer, is produced by transferring part of the transfer layer, is produced by uniformly dispersing first and second pigments in a homogeneous flowable mixture including first and second liquids, the first pigment being adapted to be held in dispersion in the flowable mixture by surface forces but unable of being held dispersed by such forces in the second liquid, and the second pigment being adapted to be held in dispersion by surface forces in the mixture and in the second liquid, followed by preferentially removing the first liquid from the mixture, whereby the first pigment is precipitated, receiving the precipitated first pigment on a substrate, and thereafter removing the second liquid thereby precipitating the second pigment, after precipitation of the first pigment.

CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of our copending application Serial No. 578,579, filed Sept. 12, 1966 and entitled Copy Sheet and Method of Making the Same and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a copy sheet and a method of making the same and, more particularly, the present invention is concerned with a copy sheet which can be inscribed or imprinted, for instance by typewriter, under simultaneous production of one or more copies without interposing carbon papers between the individual sheets.

It has been proposed to apply a transfer layer to the back face or underside of a carrier sheet. Such transfer layer may cover the entire back face of the carrier sheet or only a portion thereof. Sets of such copy papers are known for making several copies of bills, statements or the like without inserting a carbon paper or the like between the sheets on which the hand or machine-written notices are to be formed. Such papers generally include a transfer layer applied to the back face of the carrier sheet on the front face of which the original writing will be formed, for instance by typing. By superposing the back face of such sheet upon the front face of a similar sheet, and writing or forming impressions on the front face of the first sheet, a copy of such impressions is obtained on the front face of the underlying sheet.

However, the making of several copies in the last described manner without interposed carbon papers is connected with several difficulties, such as having on the back face of the original sheet a wax-like layer of dark color. Such dark layer might smear and thus soil the hands or clothing of the operator, or also other papers.

In view thereof, copy sheets were developed which have at the back face of the top sheet a transfer layer and on the front face of the underlying sheet a special take-up layer which is adapted to receive the pressure- 3,484,264 Patented Dec. 16, 1969 ice exposed portions of the transfer layer of the superposed sheet. The transfer layer is so composed in this case that it will riot smear on contact, even if such contact is under a certain degree of pressure, as long as the contacting surface is not of substantially the composition of the take-up layer.

Copy papers of the last-described type which are considered a considerable improvement over the first described papers, are disclosed, for instancme, in US. Patent 3,169,880.

However, notwithstanding the relative superiority of copy papers for instance as described in US. Patent 3,169,880, there are still certain difiiculties or disadvantages connected with the production and use thereof, particularly due to the fact that two different layers must be applied to the carrier sheets, namely transfer and take-up layers.

Thus, the carrier sheet must be passed twice through the coating machinery and this will result in an increase in production costs and reduction of the output.

Furthermore, the take-up layer consists completely of wax-like materials and this Wax-like coating closes the pores of the underlying carrier sheet so that the absorptive capacity of such carrier sheet, for instance a paper sheet is lost. Thereby direct imprinting, for'instance by means of a typewriter, or writing with ink or with a ball point pen on the take-up layer-coated paper is made difficult or impossible due to the fact that the surface of the sheet formed by a coating of the take-up layer is a poor acceptor for printing ink or writing liquid. Thus, if for instance the sheets are to be imprinted as is the case in many instances when sets of bills and the like forms are to be produced, special care must be taken or special printing inks must be used in order to obtain satisfactory imprints on the take-up layer-covered surface of the various sheets.

' It is a further disadvantage of such copy sheets and sheet assemblies that for the use thereof, for instance in order to produce an original typewritten sheet with two copies, three different types of paper must be available, namely a first sheet which is uncoatedl on its front face and carries a transfer layer on its back face, an intermediate sheet which carries a take-up layer on its front face and a transfer layer at its back face, and an underlying sheet which carries a take-up layer at its front face and need not be coated at its back face.

It is therefore an object of one of the embodiments of the present invention to provide a copy sheet which may serve for accepting the original writing, as well as for having the original writing transferred thereto without interposition of a' carbon paper or the like, which,

in a much more economical manner. Since no specialtake-up layer is required, the difliculties with respect to poor imprintability of a take-up layer-coated sheet will not occur. Furthermore, storing of supplies is facilitated since only one type of sheet is required.

The transfer layer which is preferably used according to the present invention is such that by application of pressure to a transfer layer coated carrier sheet, the pressure exposed portions of the sheet will be transferred to the contacting surface of conventional paper and the like without requiring any special treatment or coating of accepting sheet.

However, it is a disadvantage of applying such transfer layer to the copy sheets that the coating of transfer layer is of a dark or even black color. This is necessary since back face.

In view thereof, attempts have been made to produce copy sheets which consist of a colored layer which is substantially free of fat, wax or the like and wherein such colored layer is covered with a light-colored layer firmly adhering to the colored base layer. However, to produce such sheets requires two separate coating steps inasmuch as the first ink layer and then the covering layer of more acceptable color must be applied to the carrier sheet.

It has also been proposed to apply a thin, white or light-colored cover layer over a transfer layer as described for instance in US. Patent 3,169,880. The thin, white or light cover layer will cover the dark transfer layer and consequently the sheet will be of an appearance more or less comparable to that of untreated typewriter paper or the like. Here again, it is necessary to apply successively two layers to the carrier sheet so that the carrier sheet must be passed twice through the coating machine. Furthermore, it is important that the cover layer be relatively thin in order to assure that upon exertion of localized pressure the entire pressure exposed portion of the transfer layer will be transferred to the take-up layer of the underlying sheets. By thus reducing the thickness of the cover layer ,the same will possess only limited hiding power for the underlying dark colored layer.

It has also been attempted to apply the transfer layer and simultaneously therewith, or subsequently thereto, a material to lighten the color of the free surface of the transfer layer. Cellulose derivatives were used in these cases as binder for the transfer layer. It was attempted by applying a mixture of solvents and precipitating agents to achieve a whitish discoloration of the free surface portion of the transfer layer. This is known as blushing. However, only limited success has been achieved in this manner since the cellulosic binder which is responsible for the lightening is distributed throughout the entire transfer layer so that the blushing effect will occur substantially uniformly throughout the entire transfer layer and, consequently, upon transfer of pressure-exposed portions of the transfer layer to an accepting sheet the thus produced copy will also be of relatively light color. Furthermore, the thus treated transfer layers tend to smear and the lightening of the color is limited by the fact that only relatively small portions of such cellulosic binders can be incorporated.

According to another suggestion, the transfer layer has incorporated therein a dark pigment of higher specific gravity and a light pigment of lower specific gravity, preferably so that the specific gravity of the dark pigment is greater and the specific gravity of the lighter pigment is smaller than the specific gravity of the binding or dispersing agent in liquid condition. However, production of transfer sheets in this manner is rather difiicult and involved due to the fact that the transfer layer which contains the heavy and light pigments must be maintained in flowable condition for a sufiiciently long period of time until the dark pigment of higher specific gravity has settled in the zone of the surface of the supporting carrier sheet and the pigments of lesser specific gravity have risen to the surface of the suspension.

In order to facilitate this separation of the dark colored heavy pigments from the light colored pigments which are supposed to accumulate at the free surface of the transfer layer, it has been proposed to use magnetic mate- 4 rials as the heavy pigments. However, the process utilizin magnetic pigments and applying strong magnetic forces during the coating of the carrier sheet takes a considerable length of time, in other words, the coating must be maintained in sufiiciently flowable condition so as to permit relative movement of the pigments for a substantial period of time which greatly reduces the production capacity of the coating equipment.

It is therefore a further object of the present invention to overcome the various difficulties and disadvantages described hereinabove.

It is yet another object of the present invention to provide a method of producing a copy sheet of the type which requires only a single coating step and whereby the coating can be carried out at relatively high speeds, and so that a copy sheet is formed which will be lightcolored at the face formed by the transfer layer but nevertheless will produce dark copies.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

SUMMARY OF THE INVENTION According to the present invention, a transfer layer is formed of a flowable mixture which includes two different pigments which, generally, will be of different colors and, in any event, will be so chosen that one of the pigments will be held in dispersion in the mixture only as long as the mixture includes a first liquid, whereas the other of the pigments will be held in dispersion in the mixture even after removal of the first liquid therefrom. Upon removal of the first liquid it will thus be achieved that the first pigment will precipitate and, for instance by sedimentation will settle on or in the immediate vicinity of a substrate, whereas the second pigmentupon subsequent drying of, for instance a coating formed of the initial mix-. ture-will settle superposed upon the first settled pigment. The initial mixture contains additional constituents required to form a pigment-containing coating which may act as a transfer layer. Depending on the composition of the thus formed coating or transfer layer, the latter may be of the type which by pressure may be transferred to an untreated copy sheet, or may be of the type-for instance as more fully described in US. Patent 3,169,880-- which requires a specially treated receiving or copy sheet.

Preferably the above-described first and second liquids are organic solvents, and the entire pigments-containing mixture is substantially anhydrous.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional elevational view of a copy paper according to the present invention during processing of the same, after the flowable coating of transfer material has been applied to the carrier sheet but prior to drying of the transfer layer;

FIG. 2 is a cross-sectional elevational view of the completed copy paper; and

FIG. 3 is an exploded view of a three sheet assembly utilizing the copy paper according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to a preferred embodiment of the present invention, a uniform dispersion of a first pigment and of a second pigment in a homogeneous flowable mixture including a first liquid, a second liquid and a substance which is adapted to form a pressure sensitive transfer layer, is applied to a carrier sheet so as to form on the upper face of the carrier sheet a coating of the pigment dispersion in the mixture, the first pigment being held in dispersion in the mixture only in the presence of the first liquid, and the second pigment being held in dispersion in the presence of the second liquid, and the first liquid hav ing a significantly lower boiling point than the second liquid, and successively evaporating the first and second liquid from the thus formed coating so as to successively precipitate first the first pigment and thereafter the second pigment and thereby forming a transfer sheet comprising the carrier sheet and a transfer layer having the first pigment distributed substantially adjacent the carrier sheet and the second pigment adjacent to the free face of the transfer layer, which covers one face of the carrier sheet.

The present invention also includes a copy paper or the like, comprising a carrier sheet provided on one face thereof with a transfer layer adapted upon application of pressure thereto to be transferred to a contacting take-up sheet, the transfer layer having a pigment of a first color distributed through the portion thereof adjacent to the carrier sheet and having a pigment of a second color distributed through the portion thereof adjacent to the free outer face of the transfer layer, so that the face of the copy paper formed by the transfer layer will be substantially of the first color and, upon transfer of portions of the transfer layer from said copy sheet onto a take-up sheet, the free face of the transfer layer portions on the take-up sheet will be substantially of the first color.

The method of the present invention is not limited t the use of specific binding agents and it is also not necessary to use magnetic or magnetizable pigments, although such pigments may be used. Magnetizable or magnetic pigments will be used primarily when the copies formed of the pressure exposed portions of the transfer layer are to be used in data processing devices. The copy papers of the present invention are particularly suited for this purpose due to the fact that very sharp and well defined copies can be produced therefrom.

Referring now to the drawings, it will be seen that the fiowable coating when applied has dispersed therein dark and light pigments in a substantially uniform distribution.

However, as shown in FIG. 2, by proceeding in accordance with the method of the present invention, in the finished copy paper a substantial separation of the two types of pigments has taken place so that the dark pigments are predominantly located directly adjacent the carrier sheet, whereas the light pigments are predominantly located in the vicinity, of the free outer face of the transfer layer.

The carrier sheet is indicated by reference numeral 1, the flowable coating by reference numeral 2, the light colored pigments by reference numeral 4, and the dark colored pigments by reference numeral 3. The dry transfer layer is indicated in FIG. 2 by reference numeral 5.

The exploded view of FIG. 3 shows the result of form; ing an impression of exerting pressure on a portion of the uncoated upper face of the top sheet. It is accomplished thereby that portions of the transfer layer 5 of the upper and intermediate copy sheets will be transferred to the carrier layer 1 of the intermediate copy sheet and to a plain paper sheet 7 forming the bottom sheet. The transferred portions of the transfer layers 5 of the two copy sheets, i.e., the top sheet and the intermediate sheet, are indicated by reference numerals 6, and it will be immediately apparent that the upper face of the transferred portions is of dark color due to the accumulation of dark pigment in the vicinity of the upper face of the transferred portion. A typewriter key 8 is shown as the source of pressure causing the transfer of selected portions of the transfer sheets.

Copy sheets when used according to the present invention and as illustrated in FIG. 2, include a flexible carrier sheet 1, which may consist of paper or film of a synthetic polymer, and at least one pressure sensitive layer 5 which includes two substances of different color. The pressure sensitive material which forms the transfer layer is so treated according to the present invention that the lighter one of the two differently colored constituents of the transfer layer will concentrate in the zone of the free upper surface of the copy sheet and thus will mask the substance of darker color which is concentrated in the vicinity or adjacent to the carrier sheet and thus interposedbetween'the carrier sheet and the outer portion of the transfer layer which contains at least most of the substance such as pigments of lighter color. It is achieved thereby that-provided that the pigment is of substantially the same color as the carrier sheet-the copy sheet of the present invention will be of substantially the same color or color tone at the face formed by the carrier sheet and at the face formed by the transfer layer.

The separation of the two differently colored substances, particularly of lighter and darker pigments within the transfer layer is achieved according to the present invention by utilizing for producing the transfer layer the darker and lighter pigments in combination with liquids in which the constituents of the transfer layer other than the pigments are soluble or dispersable and which possess different characteristics with respect to their ability to form dispersions of the darker and lighter pigments.

The problem offorming stable pigment dispersion is a rather complicated one and so far defies complete theoretical determination, however, it is well established and known to those skilled in the art that certain pigments form stable dispersions in certain liquids whereas they precipitate when dispersed in other liquids.

In a broad sense, the forces which hold a specific pigment in suspension within a specific vehicle such as a liquid, for instance an organic solvent, may be identified as surface forces.

For instance, pigments including hydrophilic or polar groups will remain in dispersion in solvents including polar groups, and, in a similar manner, solvents or liquids of a non-polar type will be capable of forming stable suspensions of pigments having hydrophobic characteristics.

Thus, the present invention can be carried out by utilizing two differently colored pigments which differ in their hydrophilic or hydrophobic characteristics, in combination with at least two liquids or solvents which also differ in their hydrophilic or hydrophobic characteristics, whereby the wax-like constituents or binding agents are maintained in solution or dispersion in the mixture of the two solvents. If then the solvent or dispersing liquid which possesses hydrophilic characteristics similar to that of the darker colored pigment and/or dyestuffs is removed, the darker pigment or the like will be precipitated since, in the absence of the solvent of compatible hydrophilic characteristics, i.e. in the presence of only the second solvent, which differs in its hydrophilic character istics or is hydrophobic, the darker pigments cannot be maintained in suspension. Thereafter, the residual solvent or dispersing agent is removed and thereby the lighter pigment and/or dyestuffs which were maintained in suspension by the last-removed solvent, will also precipitate superposed upon the portion of the transfer layer which contains the first precipitated darker pigment.

Thus, in order to separate the pigments into the two layers of different color, pigments and solvents which preferably have different characteristics with respect to their hydrophilic or hydrophobic behavior are used. The transfer layer-forming mass contains at least two pig ments, namely one which is light or white and one which is dark or black. These two pigments differ greatly in their hydrophilic or hydrophobic characteristics. These different characteristics can be obtained either by choosing ab initio a hydrophilic and a hydrophobic pigment, or by specially treating pigments which initially do not have different characteristics in this respect, in order to give these pigments a desired degree of hydrophilic or hydrophobic characteristics.

In a very simple manner, such treatment may consist in an intensive grinding of the pigments with suitable additives, or in a precipitating of the pigments together with hydrophilic or hydrophobic materials. Pigments which in one or the other way have been treated soas to have hydrophilic or hydrophobic characteristics are well known to those skilled in the art and commercially available. They serve generally for facilitating dispersion of these pigments in different solvents or vehicles.

In many cases the degree of hydrophobic characteristics of carbon black which frequently is utilized as a dark pigment, is too low to permit separating the two different pigments with the desired speed. However, the hydrophobic characteristics of pigments such as carbon black can be increased by treating the carbon black for instance with pyrene, fluoranthene, 1,2-benzopyrene, 3,4- benzopyrene, benzoperylene, coronene; oils such as castor oil, cotton oil; ricinoleic acid, naphthenic acid or octoic acid.

On the other hand, the pigments may be endowed with hydrophilic characteristics by treatment with amides, alcohols, glycols, glycerol, pentaerythritol and the like.

Another essential feature of the present invention is the use of a mixture of vehicles or liquids or solvents, preferably organic solvents. The solvents which are suitable for the purpose of the present invention must be capable of dissolving or at least dispersing the transfer layerforming wax-like or binder constituents, or at least must not cause precipitation of binder solutions even if the concentration thereof is subsequently changed, for instance during the drying of the coating on the paper or the like support. Such solvent mixture will comprise at least two solvents, one having hydrophilic and one having hydrophobic characteristics and, furthermore, the two solvents will preferably have significantly different boiling points so that the solvent of lower boiling point can be selectively removed by heating to a temperature which is still considerably below the boiling point of the other solvent.

The mixture may also consist of more than two solvents, for instance of a mixture of several hydrophilic solvents and a mixture of several hydrophobic solvents.

The coating which is applied to the carrier sheet to form thereon, after removal of the solvents, the transfer layer may comprise the following constituents particularly if the transfer sheet is to be used in combination with a copy sheet which has not been specially treated:

(I) A wax-like material which may consist of natural and synthetic, saturated and unsaturated fatty acids and fatty acid derivatives, for instance their esters and lactones; fatty alcohols and their derivatives; natural and synthetic waxes. The wax-like material will achieve transfer of pressure exposed portions of the transfer layer onto a substrate, such as a paper which has not been specially treated for receiving portions of the transfer layer. Due to the presence of the wax-like material, the tranfser layer will be accepted upon exertion of pressure by a paper or the like which does not carry a special take-up layer. Preferably, the wax-like material will form between 10 and 70% by weight and most preferably between and by weight based on the dry weight of the entire transfer layer.

(2) The waxy material is dissolved or dispersed in the above described mixture of solvents, namely two solvents or solvent mixtures which differ from each other by their hydrophilic or hydrophobic characteristics and the boiling points of which are sufficiently far apart so that upon drying of a coating of the dispersion on a carrier sheet the major portion of one of the solvents or solvent mixtures will evaporate before the other solvent or solvent mixture starts to be volatilized to a significant extent. Thus, there should also be a sufficiently large difference between the specific heat of evaporation of the two solvents or solvent mixtures.

(3) A mixture of at least one dark or black and one white or light pigment is introduced into the above described solution of the wax-like material in the two solvents by methods which are known per se such as stirring, grinding, dispersion and the like. If the darker pigment has hydrophobic characteristics and the lighter pigment has hydrophilic characteristics, the hydrophobic solvent or solvent mixture must volatilize prior to or at lower temperature than the hydrophilic solvent or solvent mixture. However, if a dark pigment of hydrophilic characteristics is chosen and a lighter pigment of hydrophobic characteristics, then the boiling point of the hydrophilic solvent or solvent mixture must be below that of the hydrophobic solvent or solvent mixture.

The dark or black pigment preferably will be present in an amount equal to between 3 and 40% by weight of the dry transfer layer and most preferably between 9 and 15%.

The ratio between dark and light pigment depends on the relative hiding power of the individual pigments. Generally, a ratio of 1:1.5 to 1:2.5 should be maintained, however, these ratios may be exceeded in both directions. The amount of the light pigment based on the dry weight of the entire transfer layer preferably will be between 25 and 80% and most preferably between and (4) In addition, the transfer layer may also include one or more resins or synthetic polymers in order to cause firmer binding of the layer and to control the intensity of the copy formed by transfer of portions of the transfer layer. For this purpose, a great number of synthetic and natural materials may be used which are well known to those skilled in the art and which will be so chosen as to achieve the results desired in any given case. The great number of different materials which may be successfully used as binding agents or binders is indicated in the examples further below and includes for instance polystyrene, polycarbonate, polychloroprene, styrene-butadiene copolymers, polyvinylacetate, polyvinylacetal, copolymers of polyvinylacetate and polyvinylchloride and many others.

The characteristics of these binding agents may be varied within wide limits by the introduction of primary or secondary softeners and for this purpose all of the generally used conventional softeners may be employed. By specific combinations of polymers and softeners, a wide variety of characteristics of the transfer layer can be achieved in a manner which is known to those skilled in the art and not subject of the present invention.

(5) If desired, the transfer layer may additionally include fixing agents or lubricating agents which alone or jointly with the binding agents may contribute to forming an abrasion resistant transfer layer which will not give off color upon manual contact. For instance, metal soaps of saturated or unsaturated fatty acids may be used as such lubricants.

The thus obtained transfer layer-forming fiowable mass is then applied by means of conventional devices and in a conventional manner to a carrier material or substrate such as paper, a polymer foil or another suitable flexible carrier so as to form a coating of the fiowable mass on the carrier sheet.

During drying of the coating on the carrier sheet, i.e., during evaporation of the solvents or other liquids, separation of the initially homogeneous coating layer into two layers will take place.

This separation will now be explained in connection with the use of a dark pigment having hydrophobic characteristics. If the dark pigment has hydrophobic characteristics, the light pigment must have hydrophilic characteristics and the hydrophobic solvent or solvent mixture must be more easily vaporized than the hydrophilic solvent or solvent mixture. During drying of the layer, first primarily the hydrophobic solvent or solvent mixture will evaporate, until the layer contains only a relatively small proportion of the hydrophobic solvent or solvent mixture. Thereafter, the hydrophilic solvent or solvent mixture will start to be volatilized, and during the passage of still liquid hydrophilic solvent through the cross section of the coating towards the free face thereof, the hydrophilic light pigment particles will be carriedalong towards the free surface zone of the coating, since the entire hydrophilic solvent content of the drying coating has to move towards the free surface of the layer until all of the solvent is vaporized. Thereby, at the free surface of the coating, a concentration of light or white pigment will take place whereas simultaneously the portion of the coating which is directly adjacent the carrier sheet will be impoverished with respect to light or white pigment. Thus, separation into two layers will take place, namely a lighter, free surface layer portion and a darker lower transfer layer portion which is interposed between the surface portion and the carrier sheet. The other constituents of the transfer layer such as wax-like material, binder, lubricant or fixing agent are not affected by this removal of the solvents since they remain in solution or dispersion until the solvents have been vaporized, and no precipitation takes place. Thus, these other constituents of the transfer layer, i.e. the entire transfer layer with the exception of the pigments will remain homogeneously distributed and thereby it is assured that neither the transfer sheet carrying the transfer layer, nor transferred portions of the transfer layer, i.e. copies made therefrom, will smear or give up color upon manual contact.

The same effect of obtaining separation into two layers of different pigment composition is achieved by choosing a dark pigment having hydrophilic properties and a light pigment having hydrophobic properties in combination with a hydrophilic solvent or solvent mixture which will more easily vaporize than the hydrophobic solvent or solvent mixture.

A copy sheet produced in this manner has at the surface formed by the transfer layer a white or light color and nevertheless, upon forming a copy thereof by transfer of portions of the transfer layer, will give dark copies. During handling of such sheet no color will be released and no soiling :will take place upon manipulation Without undue pressure. The light color of both faces of the coy sheet, ie the face formed by the carrier sheet and the face formed by the transfer layer is also esthetically desirable.

The following examples are given as illustrative only without, however, limiting the invention to the specific details of the examples.

Example I Sixty parts by weight cyclohexane, ten parts by weight methanol, ten parts by weight microcrystalline wax having a melting point of 63-65 C. (Microwax 63, Quaker State Oil Refining Corp), ten parts by weight zinc oxide and five parts by weight kaolin are jointly ground for three hours in a ball mill together with a paste formed previously on a 3-roll grinder of two parts by weight of carbon black (Furnex Columbian Carbon Co.) and three parts by weight of polyglycol E 300 (Dow Co.). The thus formed fiowable mass is applied to a suitable sheet material by means of a doctor blade arrangement and a device which includes an arrangement for evaporating the solvent content of the fiowable mass.

Example II Forty-one parts by weight toluene, ten parts by weight acetone, ten parts by weight ethanol, ten parts by weight spermaceti wax (Archer Daniels Midland), two parts by weight hydrophilic carbon black (Colloidex No. 3, Columbian Carbon Co.) and fifteen parts by weight lithopone are ground for one hour in a ball mill. Thereafter, a solution of two parts by weight acrylic resin (Lucite 44, E. I. du Pont de Nemours) in ten parts by weight chloroform are added, thoroughly mixed and the thus formed fiowable coating material is then applied as described in Example I.

Example III Forty parts by weight xylene, twenty parts by weight isopropanol, ten parts by weight stearyl alcohol (Aldol 62, Archer Daniels Midland), four parts by weight cadmium stearate (Chem. Werke Baerlocher, Germany), eight parts by weight magnetic pigment (Magnetpigment No. 345, BASF eighteen parts by weight titanium white (Tioxide R-H-D, British Titan Products) are jointly ground in a ball mill for two hours and thereafter applied to a carrier sheet as described in Example I.

Example IV First, two parts by weight carbon black (Statex B 12, Columbian Carbon Co.) are ground on a 3-roll grinder together with three parts by weight sorbitol (Merck Co.), by being passed three times through the grinder in order to be very finely ground. The thus formed carbon black paste is then ground for one hour in a ball mill together with 65 parts by weight benzene, 5 parts by weight methanol, ten parts by weight stearic acid (Hydrofol acid 150, Archer Daniels Midland), five parts by weight calcium palmitate Baerlocher Werke, Germany) and ten parts by Weight of lithopone. The thus obtained coating material is then ready to be applied to a paper sheet or other flexible support to form upon evaporation of the solvents the copy sheet of the present invention.

Example V Fifteen parts by weight ethanol, forty parts by weight xylene, eight parts by weight hydrogenated castor oil (Castor Wax, Baker Caster Oil Co.), fifteen parts by weight titanium white, five parts by weight calcium carbonate and four parts by weight mercury sulfide are ground in a ball mill for one hour. Thereafter, a solution of three parts by weight ketone resin (Kunstharz AW 2, BASF, Germany), in ten parts by weight of xylene is added, thoroughly mixed and the thus formed mass applied to the carrier sheet by means of doctor blades.

Example VI Two parts by weight of carbon black (Spezialschwarz IV, Degussa) are finely ground on a 3-roll refiner together with two parts by weight diglucol-stearate (Atlas Goldschrnidt Ges.). Ten parts by weight of methanol, fifty parts by weight trichloroethylene, ten parts by weight 12 hydroxy-stearic acid (Hydrofol acid 200, Archer Daniels Midland) ten parts by weight lithopone, nine parts by Weight kaolin, seven parts by weight titanium white, and the above described carbon black paste are then ground in a ball mill for one hour and the thus formed coating mass is applied as described in Example I.

Pigments having hydrophobic characteristics include most types of carbon black, preferably carbon black which had been ground with oil prior to use for the present purpose. Such pigments are commercially available under various trade names such as Furnex (Columbian Carbon Co.), CK (Degussa), Printex (Degussa), Corax L and Corax B (Degussa).

Hydrophilic pigments include Aquablak (Columbian Carbon Co.), Special Black IV (Degussa), Corax 6 and Corax 7 (Degussa), Pigmosol dye stuffs of BASF such as Litholechtgruen NCR, Paliogen RT, Eisenrot G, Litholcharlach NCR, Paliogen GN, Pigmentgruen B, Farbuss 3, Titanweiss, Spin Black A, B and C (Degussa), and materials such as kaolin, lithopone and titanium white.

Organic solvents having hydrophobic characteristics include ketones, aromatic hydrocarbons such as benzene, toluene, xylene and decahydronaphthalene, aliphatic hydrocarbons such as hexene, heptene and octane, substituted hydrocarbons such as chloroform, trichloroethylene, methylene chloride and chlorobenzene, ether and polyethers such as diethyl ether and various glycol ether solvents commercially available under the trade name Poly-Solv (Olin Mathieson Chemical Corp.,) and nitrohydrocarbons.

Organic solvents having hydrophilic characteristics include aliphatic alcohols such as methanol, ethanol and isopropanol, glycols, acetone and dioxane.

Wax-like materials which may form part of the transfer layer include fatty acids and derivatives thereof such as ketocarboxy fatty acids, hydrogenated fatty acids, dicarboxy fatty acids and alkyl derivatives thereof, hydroxy fatty acids (particularly dito hexa-hydroxy), l2-hydroxy-stearic acid and alkyl esters thereof, saturated fatty acid lactones, fatty acid alkyl esters, mono-, diand triesters of fatty acids with glycerol and sorbitol, mono-fatty acids, nitro-fatty acids, polyoxyethylene fatty acids, glycols and polyglycols, for instance the products commercially available under the trade name Carbowax (Union Carbide Corporation).

Suitable wax like materials also include aliphatic alcohols and derivatives thereof, saturated alcohols as well as unsaturated alcohols, and esters thereof, 12-hydroxystearin alcohol, also waxes which are at least partially soluble in the solvents used in a given case, such as natural waxes, saturated and unsaturated hydrocarbon waxes, chlorinated and nitrated hydrocarbon waxes, cycloparafiins, ketones and hydroxy-ketones fatty acid amines, stearamide, oxidized hydrocarbon waxes, hydrogenated oils and many others.

Resins and synthetic polymers which may be incorporated in the transfer layer as binder material include also polyvinyl acetate, mixed polymerizates with polyvinyl acetate, colophonium, polymethylacrylate, polymethylmetacrylate, polycarbonate, polystyrene, polychloroprene, copolymers of styrene and butadiene, synthetic cellulose resins such as methyl, ethyl-, benzyl-, carboxymethyland nitrocellulose, coumarone resins and coumaronephenol resins.

The transfer layer may also contain a softener, for instance, castor oil, dibutylphthalate, dioctylphthalate, diamylphthalate, tricresylphosphate, cyclohexyl-p-toluene sulfonamide, dioctylsebacate, dibutylstearate, tri'butylphosphate, ricinoleic acid and many other softeners which are effective with respect to the particular binder material used in a given case.

Preferred and most preferred proportions of the constituents of the suspension which, upon evaporation of the solvents, may form the transfer layer of the present invention are indicated in the following table in which all percentage figures are given as percent by weight.

The white or lighter pigment, irrespective of whether it has hydrophobic or hydrophilic characteristics preferably should be present in a larger proportion than the dark or black pigment. Depending on the color intensity of the pigments, the ratio of light to dark pigment may vary greatly from about equal proportions of light and dark pigment to ratios of one part of dark pigment to about 50 parts of light pigment.

The following examples will serve to describe additional specific compositions of pigment dispersions which upon drying will form a transfer layer in accordance with the present invention, without limiting the invention to the specific details of these examples. I

In these examples, all percentage figures are percent by weight and (A) to (G) are intended to denote the following:

(A)Pigments having hydrophobic characteristics;

(B)Pigments having hydrophilic characteristics;

(C)-Organic solvents having hydrophobic characteristics;

(D)Organic solvents having hydrophilic characteristics; (B)Wax-like materials; (F)Binder matreials; (G)Softeners Example VII Percent Carbon black (Furnex, Columbian Car.) (A) 2 Methanol (D) 12 Methylene chloride (C) 12-hydroxystearyl alcohol (E) 10 Titanium white (B) 10 Kaolin (B) 9 Lithopone (B) 7 Example VIII Percent Printex 140 (A) 5 Titanium white (Pigmosol) (B) 20 Polyvinylacetate (F) 2 Methylene chloride (C) 30 Acetone (B) l3 Stearanilid (E) 30 Example IX Percent Carbon black (CK 3) (A) 2 Titanium white (B) 13 Kaolin (B) 8 Polystyrene (F) 2 Dioctylphthalate (G) 4 Hydrogenated castor oil (E) 12 Benzene (C) 38 Dioxane (D) 6' Example X Percent Carbon black (Corax L) (A) 6 Lithopone (B) 17 Nitrocellulose (F) 3 Castor oil (G) .i 2 Cetyl alcohol (Aldol 54) (E) 20 Methylene chloride (C) 43 Acetone (D) 13 Methanol (D) 4 Example XI Percent Carbon black (Corax L) (A) 10 Titanium white (Pigmosol) (B) 23 Ethylcellulose (F) 4 Ricinoleic acid (G) 6 Behenyl alcohol (Alcol (E) .t 21 Methylene chloride (C) 29 Ethanol (D) 7 Example XII Percent Printex 140 (A) 3 Lithopone (B) 12 Kaolin (B) 6 Stearyl alcohol (Aldol (E) 27 Methylene chloride (C) 37 Ethanol (D) 10 Isopropanol (D) 5 transfer layer will be of the type (apart from the selective pigment distribution and the two liquids) more fully de- 13 scribed in US. Patent 3,169,880. Such transfer layer may be formed for instance, of a flowable mixture including the two different pigments and the two different liquids as described above, and also including a resinous substance.

Example XIII According to another and sometimes preferred embodiment of the present invention, the two pigments-containing transfer layer will be of the type'(apart from the selective pigment distribution) more fully described in US. Patent 3,169,880. Such transfer layer may be formed, for instance on a carrier sheet, of a flowable mixture including the two different liquids and the two different pigments as described above, and also including a resinous substance selected from the group consisting of polyvinyl acetate, mixed polymerizates of polyvinyl acetate, colophonium, polymethylacrylate, polymethylmethacrylate, polycarbonates, polystyrene, polychloroprene, styrene-butadiene copolymers, synthetic cellulose resins, cumarone resin and cumarone-phenol resins, of an effective amount of at least one plasticizer for said resinous substance, of at least one organic fixing agent in an amount of between about 15-90% of the weight of said resinous substance and selected from the group consisting of tannic acid, phthalic acid, gallic acid, digallic acid, salicylic acid, phenyl salicylate, 4 butyl phenyl salicylate, 5 chloro 2 hydroxybenzophenone, 2,4-dibenzoyl-resorcin, phenol and pyrogallic acid, of at least one inorganic colloidal substance in an amount of 1.15-1.70 times the weight of said resinous substance plus said plasticizer and selected from the group consisting of bentonite, kaolin, calcium carbonate, calcium sulfate, calcium phosphate and zinc oxide, and of a pigment, whereby upon the making of an impression on the opposite face of said carrier sheet When onefacc thereof is in contact with a face of a take-up sheet sensitive to and adapted to receive said transfer layer a portion of the transfer layer corresponding to said impression is transferred to and adheres to said take-up sheet, thereby making a copy of said impression thereon.

According to the presently discussed embodiment, the coating which is applied to the carrier sheet to form thereon, after removal of the solvents, the transfer layer, generally will comprise the following constituents:

(1) One or more resins or synthetic polymers in order to cause binding of the layer and to control the intensity of the copy formed by transfer of portions of the transfer layer. For this purpose, a great number of synthetic and natural materials may be used which are well known to those skilled in the art and which will be so chosen as to achieve the results desired in any given case. The great number of different materials which may be successfully used as binding material or binder is indicated in the examples and includes, for instance polystyrene, polycarbonate, polychloroprene, styrene-butadiene-copolymers, polyvinylacetate, polyvinylacetal, copolymers of polyvinylacetate and polyvinylchloride and many others.

The characteristics of these binding agents may be varied within wide limits by the introduction of primary or secondary plasticizers and for this purpose all of the generally used conventional plasticizers may be employed. By specific combinations of polymers and plasticizers, a wide variety of characteristics ofthe transfer layer can be achieved in a manner which is, known to those skilled in the art and not subject to the present invention.

(2) The binder is dissolved or dispersed in the above described mixture of solvents, namely two solvents or solvent mixtures which differ from each other by their hydrophobic characteristics and the boiling points of which are sufficiently far apart so that upon drying of a coating of the dispersion on a carrier sheet the major portion of one of the solvents or solvent mixtures will evaporate before the other solvent or solvent mixture starts to be volatilized to a significant extent. Thus, there should also be a suflicently large difference between the specific heat of evaporation of the two solvents or solvent mixtures.

(3) A mixture of at least one dark or black and one light or white pigment is introduced into the above described solution of binder mataerial in the two solvents by methods which are known per se as stirring, grinding, dispersion and the like. If the darker pigment has hydrophobic characteristics, the hydrophobic solvent or solvent mixture must volatilize prior to or at lower temperature than the hydrophilic solvent or solvent mixture. However,

if a dark pigment of hydrophilic characteristics is chosen and a lighter pigment of hydrophobic characteristics, then the boiling point of the hydrophilic solvent orsolvent mixture must be below that of the hydrophobic solvent or solvent mixture.

The dark or black pigment preferably will be present in an amount equal to between 3 and 40% by weight of the dry transfer layer and most preferably between 9 and 15%.

The ratio between dark and light pigment depends on the relative hiding power of the individual pigments; Generally, a ratio of 1:15 to 1:25 should be maintained; however, these ratios may be exceeded in both directions. The amount of the light pigment based on the dry weight of the entire transfer layer preferably will be between 25 and and most preferably between 55 and 65%.

(4) If desired, the transfer layer may additionally include fixing agents or lubricating agents which jointly with the binding agents may contribute to forming an abrasion resistant transfer layer which will not give off color upon manual contact. For instance, metal soaps of saturated or unsaturated fatty acids may be used as such lubricants. r

The thus obtained transfer layer-forming flowable mass is then applied by means of conventional devices and in a conventional manner to a carrier sheet or substrate such as paper, a polymer foil or another suitable flexible carrier so as to form a coating of the flowable mass on the carrier sheet.

During drying of the coating on the carrier sheet, i.e., during evaporation of the solvents or other liquids, separation of the initially homogeneous coating layer into two layers will take place.

The separation of the pigments will then be carried out in the same manner as described in connection with the earlier discussed embodiment of the present invention, i.e. the embodiment according to which pressure transfer of portions of the transfer layer can be carried out onto an untreated surface.

The above'description of the last discussed embodiment particularly when taken in conjunction with the disclosure of US. Patent 3,169,880 will clearly teach those skilled in the art how to produce a transfer layer according to the present invention which is transferable only to a take-up sheet which is sensitive to and adapted to receive such transfer layer.

By way of example, hydrophilic pigments may be made hydrophobic by kneading equal amounts of channel black and of a 10 percent solution of pyrene in toluene in a closed indirectly heatable vessel. After one hour the toluene is vaporized and the residual treated channel black is usable as hydrophobic pigment for instance with titanium white as the hydrophilic pigment. Similarly carbon black may be treated with an equal amount of an 8 percent solution of naphtenic acid in benzene, or a 10 percent solution of 3-4 benzopyrene in toluene.

I-lydrophilic properties of a pigment may be improved for instance by kneading equal proportions of rutile-type titanium white containing aluminium zinc and silicon with a 3 percent aqueous solution of chlorinated starch followed by evaporation of water. Similarly titanium white 15 may be treated with a 3 percent solution of glycerol in ethanol followed by evaporation of ethanol, or by treating with a 3 percent solution of pentaerythritol in aqueous ethanol. Thus treated hydrophilic titanium white may be used in combination with carbon black made hydrophobic as described above.

A complete coating composition may be formed of an 8 percent solution of polyvinyl acetate in 90 percent ethanol as binder and including primary and secondary softeners such as 4 parts ricinoleic acid, 4 parts castor oil, 8 parts ethyl-hexyl-sebacate for 45 parts of solution. 5 parts hydrophobically treated channel black and 26 parts hydrophilically treated titanium White are ground and dispersed into the above mixture. 8 parts methylglycol are introduced for stepwise evaporation of solvents. Since in this case the black pigment is hydrophobic, ethanol must be evaporated prior to water so that the channel black will be first precipitated and the titanium white will form the upper layer.

Similarly the coating composition may be formed of a mixture of 3.6 parts polyvinyl acetate of medium polymerization degree, 20 parts 94 percent ethanol, 4 parts water and 17.4 parts acetone into which are introduced 8 parts dibutylphthalate, 4 parts amylphthalate, 4 parts castor oil, 5 parts carbon black, 5 parts kaolin, 21 parts hydrophilically treated titanium white and 8 parts isopropanol.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications Without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of forming a transfer sheet comprising the steps of uniformly dispersing a first pigment and a second pigment of a different color than said first pigment in a homogeneous fiowable mixture including a first and a second liquid and a substance which is soluble in said liquids and which is adapted to form a pressure sensitive layer, said first pigment being held in dispersion only in the presence of said first liquid and precipitating in the absence of said first liquid, and said second pigment being held in dispersion only in the presence of said second liquid and precipitating in the absence of said second liquid, said first liquid having a significantly lower boiling point than said second liquid, one of said pigments and the corresponding liquid having hydrophilic characteristics, and the other of said pigments and the other of said liquids having hydrophobic characteristics; applying said uniform dispersion to a carrier sheet so as to form on one face of said carrier sheet a coating of said pigment dispersion in said mixture; and successively evaporating said first and said second liquid from said coating so as to successively precipitate in the indicated sequence said first and second pigment, thereby forming a transfer sheet comprising said carrier sheet and a transfer layer having said first pigment substantially distributed adjacent said carrier sheet, and said second pigment adjacent to the free face of said transfer layer.

2. A method as defined in claim 1, wherein said first pigment and said first liquid have hydrophobic characteristics and said second pigment and said second liquid have hydrophilic characteristics.

3. A method as defined in claim 1, wherein said first pigment and said first liquid have hydrophilic characteristics and said second pigment and said second liquid have hydrophobic characteristics.

4. A method as defined in claim 1, wherein said substance includes a wax-like material.

5. A method as defined in claim 4, wherein said waxlike material is selected from the group consisting of saturated and unsaturated fatty acids and derivatives thereof, fatty alcohols and derivatives thereof, and natural and synthetic waxes.

6. A method as defined in claim 5, wherein said waxlike material is present in an amount equal to between 10 and 70% of the dry weight of said pigment dispersion in said mixture.

7. A method as defined in claim 5, wherein said waxlike material is present in an amount equal to between 20 and 30% of the dry weight of said pigment dispersion in said mixture.

8. A method as defined in claim 5, wherein said substance additionally includes a binder material.

9. Amethod as defined in claim 8, wherein said binder material is selected from the group consisting of polystyrene, polycarbonate, polychloroprene, styrene-butadiene copoly-mers, polyvinylacetate, polyvinylacetal, copolymers of polyvinylacetate and polyvinylchloride, and polymethylmethacrylate.

10. A method as defined in claim 1, wherein said first pigment is of darker color than said second pigment and the dry weight of said second pigment is equal to between about 1.5 and 2.5 times the dry weight of said first pigment.

11. A method as defined in claim 1, wherein said first pigment is of darker color than said second pigment and said second pigment is present in an amount equal to between 25 and of the dry weight of said mixture.

12. A method as defined in claim 1, wherein said first pigment is of darker color than said second pigment and said second pigment is present in an amount equal to between 55 and 65% of the dry weight of said mixture.

13. A method as defined in claim 1, wherein said flowable mxiture includes a resinous substance selected from the group consisting of polyvinyl acetate, mixed polymerizates of polyvinyl acetate, colophonium, polymethylacrylate, polymethylmethacrylate, polycarbonates, polystyrene, polychloroprene, styrene-butadiene copolyrners, synthetic cellulose resins, cumarone resin and cumaronephenol resins, an effective amount of at least one plasticizer for said resinous substance, and at least one organic fixing agent in an amount of between about 15-90% of the weight of said resinous substance and selected from the group consisting of tannic acid, phthalic acid, gallic acid, digallic acid, salicylic acid, phenyl salicylate, 4-butylphenyl-salicylate, 5-chloro-Z-hydroxy-benzophenone, 2,4- dibenzoyl-resorcin, phenol and pyrogallic acid.

References Cited UNITED STATES PATENTS 3,111,422 11/1963 Newman et al 1l7-36.1 3,337,361 8/1967 La Count 11736.1 3,382,088 5/1968 Noda 11736.1

FOREIGN PATENTS 906,187 9/ 1962 Great Britain.

MURRAY KATZ, Primary Examiner US. Cl. X.R. 

